Materials that are not easily burned or are non-combustible are increasingly used in the production of furniture and textiles. For example, in upholstery materials, such as fabrics, fibers that do not catch fire easily, or are non-flammable, and prevent fire are used. This kind of fibers include, inter alia, silicate-containing fibers.
One manner to manufacture silicate-containing fibers is to adapt viscose manufactured of cellulose by adding silicon dioxide to it and by spinning and processing the thus created silicate-containing fiber for further use. This kind of a method is presented, for example, in the GB patent 1064271, where the viscose-containing sodium silicate is spun into an acidic spinning solution, where the regeneration of the viscose into cellulose takes place, and at the same time, the sodium silicate in the viscose precipitates into silicon acid, which is water-containing silicon dioxide evenly distributed throughout the cellulose.
The method according to the above-mentioned patent is an inexpensive manner to manufacture silicate-containing fibers. The problem is that the silicon acid in the fibers formed by this method does not endure the alkaline detergents used in washing of textiles. In repeated washes, the silicon acid contained by the fibers dissolves into the alkaline washing liquid, which leads into a decreased fire durability.
The above-mentioned problem is solved in the FI patent 91778 (corresponds to U.S. Pat. No. 5,417,752) by processing the spun silicate-containing viscose fiber with sodium aluminate, wherein the silicon dioxide that is in silicon acid form in the silicate reacts with the aluminate and forms aluminum silicate groups in the silicon acid. The solubility of the aluminum silicate groups-containing silicon acid to alkaline detergents is very small, and therefore the product can be washed with normal detergents without its fire prevention properties being altered. In addition, the product containing aluminum silicate groups has a significantly better fire protection efficiency than products manufactured without aluminate.
The problem with the methods according to both of the above-mentioned publications is, however, the tendency of the silicate contained by the viscose, i.e. the silicon acid or silica (SiO2.nH2O) to dissolve into the spinning solution in spinning. It has been detected that a significant part of the silicate, even hundreds of milligrams/liter of spinning solution, may remain in the spinning solution in spinning. The uncontrolled dissolution of silicate and dispersion into the spinning solution causes several problems. The silicate forms precipitate in the spinning bath, which causes fouling of the spinning bath and increases friction between the tow consisting of thousands of fibers that is formed in the spinning bath and, and the stretch rolls, i.e. galets and stretch stones. Friction between individual fibers also increases in the tow, which weakens the stretchability of the tow and thus also the strength of an individual fiber. The friction between fibers also causes fibers to fray at the spinner.
The uncontrolled dissolution of silicate from the fibers into the spinning solution also causes quality fluctuations in them. This can be seen as fluctuations in the strength values and titer, i.e. the weight/length values of the fiber, which deteriorates the textile properties of the fiber. In addition, a decrease in the amount of silicate in a fiber leads to a weakened fire durability of the finished fiber, because even only a decrease of 1 to 2% in the amount of silicate deteriorates fire protection significantly.